1. Field of the Invention
This invention relates to wireline apparatus for sidewall coring in oil and gas bore holes. More particularly, this invention relates to sidewall rotary coring apparatus for obtaining large sidewall cores in bore holes.
2. Discussion of Related Art
It is common geophysical practice to collect cores from oil and gas bore holes at known depths for analyzing the core materials in order to determine various characteristics of the subterranean earth formation. In oil and gas well bore holes, it is conventional to be able to obtain sidewall cores that are usually a maximum of 1.6 inches in length and 0.9 inches in diameter. The cores are recovered and analyzed at the surface to determine the physical properties of the formation adjacent to the bore hole.
The current sidewall coring tools are complex and do not allow the coring of large sidewall cores, cores larger than the 1.6 in..times.0.9 in size mentioned above. The current tools use small high speed motors to drive the rotary coring apparatus which is not suitable in coring very hard rock formations, and have a tendency to become stuck in the formation. Most rotary sidewall coring tools have the drive motor axially aligned with the coring bit and tube which substantially limits the size of the motor and the length of the core that is obtainable in small diameter bore holes of 6 to 8 inches in diameter. Most coring tools do not have a reliable decentralizing arm system that is capable of exerting sufficient locking forces between the wall of the bore hole and the tool surface that will hold the tool in place during the coring operation, especially when the tool is coring in hard rock formations.
Accordingly, the present invention overcomes the deficiencies of the prior art by providing apparatus for rigidly anchoring the coring tool in place and an improved rotary coring apparatus for permitting the coring of large sidewall cores.